I was once faced with a tricky situation similar to yours after major renovations to the back and side yards to correct drainage problems.* I had 500 pots to sink into the ground for the winter and had hurt my back.* I placed the pots on top of the areas I wanted to sink the pots into and covered the pots and soil with old sheets.* In January, when the temps were in the teens, I was still digging and sinking pots into the soil.* Where ever I had covered the soil it wasn't frozen.* Immediately after sinking the pots, I mulched with shredded hardwood mulch that had also been covered.* So go ahead and cover your tender and/or blooming plants with a sheet when the sun goes down.* You can uncover them any time in the morning once the temps go to about 40*F.* DO NOT use plastic as the sun can heat up what's under the plastic and fry your plants.* If you forget to remove the sheets there will be no harm done.
I was never able to find a new back or neck, but my chiropractor, along with epsom salt soaks in a tub, did help alot!*
When weeding, the best way to make sure you are removing a weed and not a valuable plant is to pull on it. If it comes out of the ground easily, it is a valuable plant.